Acute neuropathological consequences of short-term mechanical ventilation in wild-type and Alzheimer's disease mice

Background: Mechanical ventilation is strongly associated with cognitive decline after critical illness. This finding is particularly evident among older individuals who have pre-existing cognitive impairment, most commonly characterized by varying degrees of cerebral amyloid-β accumulation, neuroinflammation, and blood-brain barrier dysfunction. We sought to test the hypothesis that short-term mechanical ventilation contributes to the neuropathology of cognitive impairment by (i) increasing cerebral amyloid-β accumulation in mice with pre-existing Alzheimer's disease pathology, (ii) increasing neurologic and systemic inflammation in wild-type mice and mice with pre-existing Alzheimer's disease pathology, and (iii) increasing hippocampal blood-brain barrier permeability in wild-type mice and mice with pre-existing Alzheimer's disease pathology.

Methods: We subjected double transgenic Alzheimer's disease (APP/PSEN1) and wild-type mice to mechanical ventilation for 4 h and compared to non-mechanically ventilated Alzheimer's disease model and wild-type mice. Cerebral soluble/insoluble amyloid-β_1-40/amyloid-β_1-42 and neurological and systemic markers of inflammation were quantified. Hippocampal blood-brain barrier permeability was quantified using a novel methodology that enabled assessment of small and large molecule permeability across the blood-brain barrier.

Results: Mechanical ventilation resulted in (i) a significant increase in cerebral soluble amyloid-β_1-40 (p = 0.007) and (ii) significant increases in neuroinflammatory cytokines in both wild-type and Alzheimer's disease mice which, in most cases, were not reflected in the plasma. There were (i) direct correlations between polymorphonuclear cells in the bronchoalveolar fluid and cerebral soluble amyloid-β_1-40 (p = 0.0033), and several Alzheimer's disease-relevant neuroinflammatory biomarkers including cerebral TNF-α and IL-6; (iii) significant decreases in blood-brain barrier permeability in mechanically ventilated Alzheimer's disease mice and a trend towards increased blood-brain barrier permeability in mechanically ventilated wild-type mice.

Conclusions: These results provide the first evidence that short-term mechanical ventilation independently promotes the neuropathology of Alzheimer's disease in subjects with and without pre-existing cerebral Alzheimer's disease pathology. Future studies are needed to further clarify the specific mechanisms by which this occurs and to develop neuroprotective mechanical ventilation strategies that mitigate the risk of cognitive decline after critical illness.